A reading of 100 is considered healthy. The last time the index reached that high was in April 2010, the final month that buyers could qualify for a federal tax credit that has since expired.

Contract signings are usually a reliable indicator of where the housing market is headed. There’s typically a one- to two-month lag between a contract and a completed deal.

But the Realtors group said a growing number of buyers have canceled contracts after appraisals showed that the homes were worth less than the buyers had bid. A sale isn’t final until a mortgage is closed. That means more “pending” sales aren’t turning into final sales.

“It is especially troubling given the big August decline in long-term interest rates,” said Pierre Ellis, an analyst at Decision Economics.

Homes are the most affordable they’ve been in decades. Long-term mortgage rates are hovering at record lows near 4 percent. Prices in some metro areas have been cut in half. Still, sales in most areas remain weak.

In part, that’s because loans are harder to get. Many lenders are requiring 20 percent down payments and strong credit scores to qualify.

Sales for previously occupied homes are on pace to match last year’s 4.91 million sold, the fewest since 1997. In a healthy economy, Americans would buy roughly 6 million homes each year.

In September, sales of new homes rose after four straight monthly declines. But that was largely because builders had cut their prices in the face of depressed demand. This year is shaping up as the worst for new-home sales on records dating to 1963.

The number of people who signed home contracts had risen in both May and June before falling 7 percent over the past three months.

Contract signings fell across the U.S. September’s index fell 2.1 percent in the West, 4.7 percent in the Northeast, 5.5 percent in the South and 6.2 percent in the Midwest.